When do you consider repeating an autoimmune encephalopathy work up if initial MRI, LP, and paraneoplastic panel antibodies are non-revealing?

This is highly dependent on the specific clinical scenario and my pre-test probability of autoimmune encephalitis. Tools like APE2 help provide a framework for assessing how likely a positive result on antibody panel at the time of initial presentation. If the initial workup with MRI, basic CSF studies, and both serum and CSF antibody panels are negative, I would start by rethinking the possible diagnoses and broadening my differential diagnosis/workup.

If immunotherapy is given and the patient demonstrates a clear response, I would consider repeating MRI, serum and CSF antibody panel testing, and malignancy screening in a few months. I would also certainly repeat these tests if relapsing symptoms occur months after immunotherapy.